In the multiple antenna radio communication devices, antenna calibration (AC) circuits are often integrated with the antenna transmission (TX)/receiving (RX) circuits on the TX/RX board (also referred to as TRXB). In Time Division Duplex (TDD) device, the antenna TX frequency is equal to the antenna RX frequency, while in Frequency Division Duplex (FDD) device, the antenna TX frequency differs from the antenna RX frequency. In prior art, due to the differences above, TDD device and FDD device have to be configured with different antenna calibration circuits.
Generally, the TDD device utilizes the antenna calibration circuit as shown in FIG. 1, where the RX circuit 110 and the TX circuit 120 for the antenna 101 can be also configured to operate as the calibration circuit. The process of antenna TX calibration is illustrated in the FIG. 1. The dash lines show the flow path of the TX calibration signal to be transmitted by the individual antennas, and all the transmitted signals are received through the calibration circuit path illustrated by the solid line, such that the reception of the transmitted signal can be used for the TX calibration of the multiple antennas.
On the other hand, since the TX frequency and RX frequency are in the different frequency band in FDD system, the FDD device may be designed with the calibration circuit as shown in FIG. 2, where an extra dedicated calibration TX/RX path is added. In the calibration path, the RX frequency of the RX calibration path is consistent with the TX frequency of the FDD device antennas. In this way, the antenna TX calibration can be performed along the flow path as shown in the FIG. 2. Likewise, in the calibration path, the TX frequency of the TX calibration path needs to be consistent with the RX frequency of the FDD device antennas for the antenna RX calibration.
In addition, the FDD device may also be designed with the calibration circuit as shown in FIG. 3, where the extra calibration TX/RX path is not introduced, nevertheless a mixer 390 is still needed, which is used to remedy the gap of the antenna TX/RX frequency during the antenna calibration.
The disadvantages in the existing solution are obvious:
1) The TDD and FDD devices are using different hardware solution for the antenna calibration. In that case, they can't share the same hardware design. Accordingly, the software has to be modified because of the difference;
2) The solution for FDD is more complicated than TDD. In the solution as shown in FIG. 2, it has to involve a dedicated RX/TX calibration path to handle the function, which increases the cost and also consumes more layout area on the TRXB. In the solution as shown in FIG. 3, the additional mixer introduces a further undesirable nonlinearity, which will impact the accuracy of calibration result.